Prepreg, metal-clad laminate and printed circuit board using same

ABSTRACT

This invention provides a prepreg which can yield printed circuit boards with excellent dimensional stability and heat resistance and the ability to be bent and housed at high density in electronic device packages, by impregnating a thin fiber base material with a resin having excellent adhesion with metal foils or fiber base materials, excellent heat resistance and high pliability, as well as a metal foil-clad laminate and printed circuit board employing it. The prepreg of the invention is obtained by impregnating a resin composition containing a resin with an imide structure and a thermosetting resin into a fiber base material with a thickness of 5-50 μm.

This application is a Divisional application of application Ser. No.10/591,696, having a date of completion of requirements under 35 USC 371of Jul. 16, 2007, the contents of which are incorporated herein byreference in their entirety. No. 10/591,696 is a National StageApplication, filed under 35 USC 371, of International (PCT) ApplicationNo. PCT/JP2005/03753, filed Mar. 4, 2005.

TECHNICAL FIELD

The present invention relates to a prepreg and to a metal foil-cladlaminate and printed circuit board that employ it.

BACKGROUND ART

Laminates for printed circuit boards are formed by stacking a prescribednumber of prepregs comprising an electrical insulating resin compositionas the matrix, and subjecting them to heat and pressure for integration.

Metal-clad laminates are used for formation of printed circuits by asubtractive process. Metal-clad laminates are fabricated by stacking ametal foil such as copper foil on a surface (either or both surfaces) ofa prepreg and subjecting the stack to heat and pressure. As electricalinsulating resins there are commonly used thermosetting resins such asphenol resins, epoxy resins, polyimide resins, bismaleimide-triazineresins and the like. Thermoplastic resins such as fluorine resins orpolyphenylene ether resins are also sometimes used.

On the other hand, with the increasing popularity of data terminaldevices such as personal computers and cellular phones there is a trendtoward miniaturization and high-densification of the printed circuitboards mounted therein. The mounting methods are advancing frompin-insertion types to surface-mounted types, and also to area arraytypes of which BGA (ball grid arrays) using plastic boards are a typicalexample. In boards where bare chips such as BGA are directly mounted,connection between the chips and boards is commonly achieved by wirebonding using thermosonic bonding. In such cases, the board on which thebare chip is mounted is exposed to high temperatures of 150° C. andabove, and therefore the electrical insulating resin must have somedegree of heat resistance.

As lead-free solders become more common for environmental reasons, themelting points of solders are increasing as a result. Thus, even higherheat resistance is demanded for boards. Demand for halogen-freematerials is also increasing, thus precluding the use of bromine-basedflame retardants.

Moreover, for printed circuit boards, the “repair properties” allowingmounted chips to be removed are often required. During repair, theboards are subjected to about the same level of heating as during chipmounting, after which further heat treatment is carried out forremounting of chips. Such treatment has often resulted in peelingbetween the fiber material and resin in conventional insulating resinsystems. Thus, boards exhibiting repair properties must also havecycling heat shock-resistant properties at high temperatures.

Prepregs have been proposed that exhibit excellent heat shockresistance, reflow resistance and crack resistance, and improvedmicrowiring formation properties, by impregnating a resin compositioncomprising a polyamideimide as an essential component into the fibermaterial (see Japanese Unexamined Patent Publication No. 2003-55486).

Also, with the trend toward greater miniaturization and higherperformance of electronic devices, it is becoming necessary to housepart-mounted printed circuit boards in increasingly limited spaces. Thisis accomplished by methods of arranging multiple printed circuit boardsin stacks and connecting them alternately with wire harnesses orflexible wiring boards. There are also used rigid-flex boards which arelayered combinations of polyimide-based flexible boards and conventionalrigid boards.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been accomplished in light of the problems ofthe prior art described above, and its object is to provide a prepregwhich can yield printed circuit boards with excellent dimensionalstability and heat resistance and the ability to be bent and housed athigh density in electronic device packages, by impregnating a thin fiberbase material with a resin having excellent adhesion with metal foils orfiber base materials, excellent heat resistance and high pliability, aswell as a metal foil-clad laminate and printed circuit board employingit.

Means for Solving the Problems

In order to achieve the aforestated object, the prepreg of the inventionis characterized by comprising a resin composition containing a resinwith an imide structure and a thermosetting resin, impregnated into afiber base material with a thickness of 5-50 μm.

In this prepreg, the resin with an imide structure is more preferablyone having a siloxane structure.

The resin with an imide structure may also be one having the structurerepresented by the following general formula (1).

The resin with an imide structure is more preferably a polyamideimideresin.

More specifically, the resin with an imide structure is preferably apolyamideimide resin obtained by reacting a diisocyanate compound with amixture containing a diimidedicarboxylic acid obtained by reacting amixture containing a siloxanediamine and a diamine represented by thefollowing general formula (2a) or (2b) with trimellitic anhydride.

[wherein X²¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, a single bond, a divalent group represented by thefollowing general formula (3a) or a divalent group represented by thefollowing general formula (3b), X²² represents a C1-3 aliphatichydrocarbon group, C1-3 halogenated aliphatic hydrocarbon group,sulfonyl group, ether group or carbonyl group, and R²¹, R²² and R²³ eachindependently or identically represent hydrogen, hydroxyl, methoxy,methyl or halogenated methyl.

(wherein X³¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group,carbonyl group or a single bond.)]

The resin with an imide structure may also be a polyamideimide resinobtained by reacting a diisocyanate compound with a mixture containing adiimidedicarboxylic acid obtained by reacting a mixture containing adiamine represented by the following general formula (4), asiloxanediamine and a diamine represented by the following generalformula (5a) or (5b), with trimellitic anhydride.

[wherein X⁵¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, a single bond, a divalent group represented by thefollowing general formula (6a) or a divalent group represented by thefollowing general formula (6b), X⁵² represents a C1-3 aliphatichydrocarbon group, C1-3 halogenated aliphatic hydrocarbon group,sulfonyl group, ether group or carbonyl group, and R⁵, R⁵² and R⁵³ eachindependently or identically represent hydrogen, hydroxyl, methoxy,methyl or halogenated methyl.

(wherein X⁶¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, or a single bond.)]

The resin with an imide structure may also be a polyimide resin havingthe structure represented by the following general formula (7) or apolyimide resin having the structure represented by the followinggeneral formula (7) and the structure represented by the followinggeneral formula (8).

[wherein Ar¹ represents a tetravalent aromatic group, Ar² represents adivalent aromatic group, R⁷¹ and R⁷² each independently or identicallyrepresent a divalent hydrocarbon group, R⁷³, R⁷⁴, R⁷⁵ and R⁷⁶ eachindependently or identically represent a C1-6 hydrocarbon group, and nrepresents an integer of 1-50.]

Also, the resin with an imide structure may be a polyamideimide resinhaving the structure represented by the following general formula (9).Such a polyamideimide resin includes the structure represented bygeneral formula (1) above in the molecule.

[wherein R⁹¹, R⁹², R⁹³ and R⁹⁴ each represent a carbon atom from aportion of the cyclic or linear structure composing the polyamideimideresin.]

The thermosetting resin in the resin composition of the prepreg of theinvention is preferably an epoxy resin. More preferred are epoxy resinshaving two or more glycidyl groups.

The resin composition preferably further contains aphosphorus-containing compound, in which case the resin compositionpreferably contains the thermosetting resin at 1-140 parts by weightwith respect to 100 parts by weight of the resin with an imidestructure, and phosphorus at 0.1-5 wt % of the resin solid portion.

The resin composition even more preferably further contains a hinderedphenol-based or organic sulfur compound-based antioxidant.

As such antioxidants there are preferred one or more types selected fromthe group consisting of butylated hydroxyanisole,2,6-di-t-butyl-4-ethylphenol,2,2′-methylene-bis(4-methyl-6-t-butylphenol),4,4′-thiobis-(3-methyl-6-t-butylphenol),4,4′-butylidenebis(3-methyl-6-t-butylphenol),1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenylpropionate)methane,dilauryl thiodipropionate and distearyl thiodipropionate.

The prepreg of the invention preferably has a combustion distance of nogreater than 100 mm in a UL-94 VTM test, when cured to form a basematerial.

The invention further provides a metal foil-clad laminate obtained usingthe aforementioned prepreg of the invention. Specifically, the metalfoil-clad laminate of the invention is obtained by stacking a prescribednumber of prepregs of the invention, situating a metal foil on either orboth sides and subjecting them to heat and pressure.

The invention further provides a printed circuit board obtained usingthe aforementioned metal foil-clad laminate of the invention.Specifically, the printed circuit board of the invention is obtained bycircuit formation on the metal foil of the metal foil-clad laminate ofthe invention.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a partial perspective view of an embodiment of a prepreg.

FIG. 2 is a partial cross-sectional view of an embodiment of a metalfoil-clad laminate.

FIG. 3 is a partial cross-sectional view of an embodiment of a printedcircuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the invention will now be explained in detail,with reference to the accompanying drawings as necessary.

[Prepreg]

The prepreg will be explained first. The prepreg of this embodiment isobtained by impregnating a resin composition containing a resin with animide structure and a thermosetting resin into a fiber base materialwith a thickness of 5-50 μm. The components in the resin compositionwill be explained first.

(Resin with an Imide Structure)

The resin with an imide structure is a compound having at least oneimide structure in the molecule, and preferred examples includepolyamideimide resins, polyimide resins and maleimide resins.

Polyamideimide resins will be described first. A polyamideimide resin isa resin containing an imide group and an amide group in the repeatingunit. Suitable polyamideimide resins include siloxane-modifiedpolyamideimide resins having a siloxane structure in the repeating unit.

Preferred as such polyamideimide resins with a siloxane structure arethose obtained by reacting an aromatic diisocyanate with a mixturecontaining a diimidedicarboxylic acid which is obtained by reacting amixture containing a siloxanediamine and a diamine with two or morearomatic rings represented by general formula (2a) or (2b) above(aromatic diamine) with trimellitic anhydride.

For synthesis of a siloxane-modified polyamideimide resin with asiloxane structure, the blending ratio of the diamine a with two or morearomatic rings and the siloxanediamine b is preferablya/b=99.9/0.1-0/100 (molar ratio), more preferably a/b=95/5-30/70 andeven more preferably a/b=90/10-40/60. If the blending proportion of thesiloxanediamine b is too large, the Tg will tend to be reduced. If it istoo small, on the other hand, a larger amount of varnish solvent willtend to remain in the resin from production of the prepreg.

Examples of aromatic diamines include2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP),bis[4-(3-aminophenoxy)phenyl]sulfone,bis[4-(4-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,bis[4-(4-aminophenoxy)phenyl]methane, 4,4′-bis(4-aminophenoxy)biphenyl,bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ketone,1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene,2,2′-dimethylbiphenyl-4,4′-diamine,2,2′-bis(trifluoromethyl)biphenyl-4,4′-diamine,2,6,2′,6′-tetramethyl-4,4′-diamine,5,5′-dimethyl-2,2′-sulfonyl-biphenyl-4,4′-diamine,3,3′-dihydroxybiphenyl-4,4′-diamine, (4,4′-diamino)diphenyl ether,(4,4′-diamino)diphenylsulfone, (4,4′-diamino)benzophenone,(3,3′-diamino)benzophenone, (4,4′-diamino)diphenylmethane,(4,4′-diamino)diphenyl ether and (3,3′-diamino)diphenyl ether.

As siloxanediamines there may be mentioned compounds represented by thefollowing general formulas (10a)-(10d).

Examples of siloxanediamines represented by general formula (10a) aboveinclude X-22-161AS (450 amine equivalents), X-22-161A (840 amineequivalents), X-22-161B (1500 amine equivalents) (all products ofShin-Etsu Chemical Co., Ltd.), BY16-853 (650 amine equivalents) andBY16-853B (2200 amine equivalents) (all products of Dow Corning ToraySilicone Co., Ltd.). Examples of siloxanediamines represented by generalformula (10d) above include X-22-9409 (700 amine equivalents) andX-22-1660B-3 (2200 amine equivalents) (both products of Shin-EtsuChemical Co., Ltd.).

As diisocyanate compounds to be used for production of polyamideimideresins there may be mentioned compounds represented by the followinggeneral formula (11).

[Chemical Formula 11]

OCN-D-NCO  (11)

In formula (11), D is a divalent organic group with at least onearomatic ring, or a divalent aliphatic hydrocarbon group, and it ispreferably at least one group selected from the group consisting of—C₆H₄—CH₂—C₆H₄—, tolylene, naphthylene, hexamethylene,2,2,4-trimethylhexamethylene and isophorone.

As diisocyanate compounds represented by general formula (11) abovethere may be used aliphatic diisocyanate or aromatic diisocyanatecompounds, but aromatic diisocyanate compounds are preferred, andcombinations of both are especially preferred.

Examples of aromatic diisocyanate compounds include4,4′-diphenylmethanediisocyanate (MDI), 2,4-tolylenediisocyanate,2,6-tolylenediisocyanate, naphthalene-1,5-diisocyanate, 2,4-tolylenedimer and the like, with MDI being particularly preferred. Using MDI asan aromatic diisocyanate can improve the flexibility of the obtainedpolyamideimide resin.

Examples of aliphatic diisocyanate compounds include hexamethylenediisocyanate, 2,2,4-trimethylhexamethylene diisocyanate and isophoronediisocyanate.

When an aromatic diisocyanate and aliphatic diisocyanate are used incombination, the aliphatic diisocyanate is preferably added at about5-10 mol % with respect to the aromatic diisocyanate. Such use incombination can further improve the heat resistance of the obtainedpolyamideimide resin.

Also suitable as polyamideimide resins to be included in the resincomposition are polyamideimide resins having a structure containingaliphatic rings as represented by general formula (1) above. Preferredamong these are polyamideimide resins having both the aforementionedsiloxane structure and a structure containing aliphatic rings. Such apolyamideimide resin includes the structure represented by generalformula (9) above.

Preferred as polyamideimide resins having both a siloxane structure anda structure containing aliphatic rings, are those obtained by reacting adiisocyanate compound with a mixture containing a diimidedicarboxylicacid obtained by reacting a mixture containing an alicyclic diamineincluding an aliphatic ring represented by general formula (4) above, asiloxanediamine and a diamine with two or more aromatic ringsrepresented by general formula (5a) or (5b) above (aromatic diamine),with trimellitic anhydride.

The alicyclic diamine represented by general formula (4) above is4,4′-diaminodicyclohexylmethane, and this compound is available, forexample, as WONDAMINE (trade name of New Japan Chemical Co., Ltd.).Examples for the siloxanediamine and aromatic diamine to be used for thereaction include the same compounds mentioned above. For synthesis of apolyamideimide resin having both a siloxane structure and a structurecontaining aliphatic rings, preferably the blending ratio of the diaminea represented by general formula (4) above (a: moles), and the total ofthe other diamine with two or more aromatic rings and thesiloxanediamine (b: moles) is a/b=0.1/99.9-99.9/0.1 (molar ratio), morepreferably it is a/b=10/90-50/50, and even more preferably it is a/b20/80-40/60.

For production of a polyamideimide containing the aforementionedsiloxane structure and/or a structure represented by general formula(1), there may also be used an aliphatic diamine in addition to thesiloxanediamine, aromatic diamine, alicyclic diamine, etc. Examples ofsuch aliphatic diamines include compounds represented by the followinggeneral formula (12).

In formula (12), X¹²¹ represents methylene, sulfonyl, ether, carbonyl ora single bond, R¹²¹ and R¹²² each represent hydrogen, alkyl, phenyl orsubstituted phenyl, and p represents an integer of 1-50.

As specific examples of R¹²¹ and R¹²² there are preferred hydrogen, C1-3alkyl, phenyl and substituted phenyl, and examples of substituentsbonded to phenyl include C1-3 alkyl, halogens and the like. From thestandpoint of achieving both a low elastic modulus and high Tg, thealiphatic diamine is preferably one wherein X¹²¹ in general formula (12)above is an ether group.

Examples of such aliphatic diamines include JEFFAMINE D-400 (400 amineequivalents) and JEFFAMINE D-2000 (1000 amine equivalents) (both tradenames of San Techno Chemical Co., Ltd.).

As the aforementioned polyamideimide resins there are preferredpolyamideimide resin containing at least 70 mol % of a polyamideimidemolecule having 10 or more amide groups in a molecule. The range can bedetermined from a chromatogram obtained from GPC (gel permeationchromatography) of the polyamideimide, and from the moles of amidegroups per unit weight (A) calculated separately. For example, where themolecular weight (C) of the polyamideimide containing 10 amide groups ineach molecule is 10×a/A based on the number of moles (A) of amide groupsin the polyamideimide (a)_(g), and at least 70% of the regions have anumber-average molecular weight of C or greater based on thechromatogram obtained by GPC, this corresponds to a content of at least70 mol % of polyamideimide molecules containing 10 or more amide groupsper molecule. The method of quantitating the amide groups may be NMR,IR, hydroxamic acid-iron color reaction, the N-bromoamide method or thelike.

The polyimide resin will now be explained. A polyimide resin is a resincontaining an imide structure in the repeating unit. As polyimide resinsthere are preferred those further including a siloxane structure in therepeating unit, and more preferred are polyimide resins having astructure represented by general formula (7) above or having a structurerepresented by general formula (7) above and a structure represented bygeneral formula (8) above. Such polyimide resins can be obtained byreacting diamine compounds with tetracarboxylic acid dianhydrides.

Siloxanediamines may be mentioned as diamine compounds for obtainingpolyimide resins with a structure represented by general formula (7)above. Examples of siloxanediamines include the same compounds used forproduction of the aforementioned polyamideimide resins.

As diamine compounds for obtaining polyimide resins having both astructure represented by general formula (7) above and a structurerepresented by general formula (8) above there may be mentionedcombinations of siloxanediamines and aromatic diamines. Assiloxanediamines there may be mentioned the same compounds used forproduction of the aforementioned polyamideimide resins. Examples ofaromatic diamines include m-phenylenediamine, p-phenylenediamine,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, benzidine,4,4′-diaminodiphenylsulfide, 4,4′-diaminodiphenylsulfone,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenyl ether,4,4′-diamino-p-terphenyl, 2,2-bis[4-(4-aminophenoxy)phenyl]propane(BAPP), bis[4-(3-aminophenoxy)phenyl]sulfone,bis[4-(4-aminophenoxy)phenyl]sulfone,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane,bis[4-(4-aminophenoxy)phenyl]methane, 4,4′-bis(4-aminophenoxy)biphenyl,bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ketone,1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene,2,2′-dimethylbiphenyl-4,4′-diamine,2,2′-bis(trifluoromethyl)biphenyl-4,4′-diamine,2,6,2′,6′-tetramethyl-4,4′-diamine,5,5′-dimethyl-2,2′-sulfonyl-biphenyl-4,4′-diamine,3,3′-dihydroxybiphenyl-4,4′-diamine, (4,4′-diamino)diphenyl ether,(4,4′-diamino)diphenylsulfone, (4,4′-diamino)benzophenone,(3,3′-diamino)benzophenone, (4,4′-diamino)diphenylmethane,(4,4′-diamino)diphenyl ether and 3,3′-diaminodiphenyl ether.

When using a combination of a siloxanediamine and an aromatic diamine,the blending ratio of the aromatic diamine “a” and the siloxanediamine“b” is preferably a/b=99.9/0.1-0/100 (molar ratio), more preferablya/b=95/5-30/70 and even more preferably a/b=90/10-50/50. If the blendingproportion of the siloxanediamine “b” is too large, the Tg will tend tobe reduced. If it is too small, on the other hand, a larger amount ofvarnish solvent will tend to remain in the resin composition fromproduction of the prepreg.

Examples of tetracarboxylic acid dianhydrides include3,3′,4,4′-diphenylethertetracarboxylic dianhydride,3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride,2,2′,3,3′-benzophenonetetracarboxylic dianhydride,3,3′,4,4′-biphenyltetracarboxylic dianhydride,2,3,3′,4′-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,1,4,5,6-naphthalenetetracarboxylic dianhydride,3,4,9,10-perylenetetracarboxylic dianhydride,3,3,6,7-anthracenetetracarboxylic dianhydride,1,2,7,8-phenanthrenetetracarboxylic dianhydride and4,4′-(hexafluoroisopropylidene)phthalic dianhydride.

The maleimide resin will now be explained. As maleimide resins there maybe mentioned those obtained by reacting a diamine compound and maleicanhydride at a molar ratio of 1:2 to form a bismaleimide, and thenmixing this with a triazine or another thermosetting resin. Examples ofdiamine compounds include the same compounds mentioned above.

(Thermosetting Resin)

As thermosetting resins to be used for the invention there may bementioned epoxy resins, polyimide resins, unsaturated polyester resins,polyurethane resins, bismaleimide resins, triazine-bismaleimide resinsand phenol resins. For example, when using a polyamideimide resin as theresin with an imide structure, the thermosetting resin is preferablyused at 1-200 parts by weight and more preferably 1-140 parts by weightwith respect to 100 parts by weight of the polyamideimide resin.

As thermosetting resins there are preferred those having organic groupsthat can react with the amide groups of the polyamideimide resin.Particularly preferred as polyamideimide resins are siloxane-modifiedpolyamideimide resins as mentioned above, in which case thethermosetting resin is preferably one having organic groups that canreact with the amide groups in the siloxane-modified polyamideimideresin. More specifically, there are preferred glycidyl group-containingepoxy resins. If the content of the thermosetting resin is less than 1part by weight to 100 parts by weight of the polyamideimide resin, thesolvent resistance will tend to be inferior. On the other hand, if itexceeds 200 parts by weight the Tg will be lower due to the unreactedthermosetting resin, leading to insufficient heat resistance andundesirable reduction in flexibility. Thus, the content of thethermosetting resin is more preferably 3-100 parts by weight and evenmore preferably 10-60 parts by weight to 100 parts by weight of thepolyamideimide resin.

As epoxy resins there may be mentioned polyglycidyl ethers obtained byreacting epichlorhydrin with a polyhydric phenol such as bisphenol A, anovolac-type phenol resin or an orthocresol/novolac-type phenol resin orwith a polyhydric alcohol such as 1,4-buthane diol, polyglycidyl estersobtained by reacting epichlorhydrin with a polybasic acid such asphthalic acid or hexahydrophthalic acid, N-glycidyl derivatives ofcompounds with amine, amide or heterocyclic nitrogenous bases, andalicyclic epoxy resins.

By using an epoxy resin as the thermosetting resin, it is possible tocure the prepreg at a temperature of below 180° C. In order to furtherimprove the thermal, mechanical and electrical properties by reactionwith the amide groups of the siloxane-modified polyamideimide resin, itis preferred to use as the epoxy resin a combination of an epoxy resinwith two or more glycidyl groups and its curing agent, a combination ofan epoxy resin with two or more glycidyl groups and its curingaccelerator, or a combination of an epoxy resin with two or moreglycidyl groups and its curing agent and curing accelerator. A greaternumber of glycidyl groups is preferred, with 3 or more being morepreferred. The content of the thermosetting resin will differ dependingon the number of glycidyl groups, and the content may be lower with alarger number of glycidyl groups.

The curing agent and curing accelerator for the epoxy resin are notparticularly restricted so long as they react with the epoxy resin orpromote its curing, and there may be used, for example, amines,imidazoles, polyfunctional phenols, acid anhydrides and the like. Asamines there may be used dicyandiamide, diaminodiphenylmethane,guanylurea and the like. As polyfunctional phenols there may be usedhydroquinone, resorcinol, bisphenol A and their halogenated forms, aswell as novolac-type phenol resins and resol-type phenol resins that arecondensates with formaldehyde. As acid anhydrides there may be usedphthalic anhydride, benzophenonetetracarboxylic dianhydride, methylhymicacid and the like. As curing accelerators there may be used imidazolessuch as alkyl-substituted imidazoles and benzimidazoles.

The preferred amount of such a curing agent or curing accelerator is, inthe case of an amine, an amount such that the equivalents of activehydrogen of the amine and epoxy equivalents of the epoxy resin areapproximately equal. For an imidazole as the curing accelerator there isno simple equivalent ratio with active hydrogen, and the amount ispreferably 0.001-10 parts by weight to 100 parts by weight of the epoxyresin. In the case of a polyfunctional phenol or acid anhydride, therequired amount is 0.6-1.2 equivalents of phenolic hydroxyl or carboxylgroups with respect to one equivalent of the epoxy resin. A small amountof such a curing agent or curing accelerator will leave some amount ofuncured epoxy resin and will lower the Tg (glass transitiontemperature), while a large amount will leave some amount of unreactedcuring agent and curing accelerator, thereby lowering the insulatingproperty. Since the epoxy equivalents of the epoxy resin can also reactwith the amide groups of the siloxane-modified polyamideimide resin,this is preferably taken into account.

(Other Components)

The resin composition may also contain other components in addition tothe aforementioned resin with an imide structure and the thermosettingresin. As examples of such additional components there may be mentionedphosphorus-containing compounds.

A phosphorus-containing compound can improve the flame retardance of theprepreg, and specifically phosphorus-based flame retardants(phosphorus-containing fillers) are preferred. As phosphorus-based flameretardants there may be mentioned OP930 (product of Clariant Japan,phosphorus content: 23.5 wt %), HCA-HQ (product of Sanko Co., Ltd.,phosphorus content: 9.6 wt %), and the melamine polyphosphates PMP-100(phosphorus content: 13.8 wt %), PMP-200 (phosphorus content: 9.3 wt %)and PMP-300 (phosphorus content: 9.8 wt %) (all products of NissanChemical Industries, Ltd.).

A larger amount of phosphorus-based flame retardant added as aphosphorus-containing compound will improve the flame retardance, but ifit is too large the pliability of the base material will be reduced andthe printed circuit board obtained therefrom will have reduced heatresistance. The amount of phosphorus-based flame retardant to be addedwill differ depending on the type and thickness of the fiber basematerial impregnated with the resin composition, and for example, whenusing a fiber base material with a thickness of 5-50 μm (such as a glasscloth) in a prepreg as described hereunder, it is preferred to adjustthe amount so that the laminate produced from the prepreg has acombustion distance of no greater than 100 mm in the UL-94 VTM test.Such a laminate exhibits sufficient properties from the standpoint ofpliability, while also exhibiting satisfactory properties in terms ofheat resistance in a heat shock test.

When the resin composition contains a polyamideimide and a thermosettingresin as described above, the amide groups and imide groups in thepolyamideimide can be utilized as a nitrogen source for flameretardance. In this case, the amount of the phosphorus-containingcompound such as a phosphorus-based flame retardant added to the resincomposition is such for a phosphorus content of preferably 0.1-5 wt %and more preferably 2-4 wt % of the total solid weight of the resin ofthe resin composition. The phosphorus-based flame retardant content maytherefore be determined in consideration of the amount of phosphoruscontained therein.

One or more antioxidants from among hindered phenol-based antioxidantsand organic sulfur compound-based antioxidants may also be included inthe resin composition. For example, using a hindered phenol-basedantioxidant can improve the electrical insulating characteristicswithout impairing the other properties such as drill working properties.

Hindered phenol-based antioxidants include monophenol-based antioxidantssuch as butylated hydroxyanisole and 2,6-di-t-butyl-4-ethylphenol,bisphenol-based antioxidants such as2,2′-methylene-bis-(4-methyl-6-t-butylphenol),4,4′-thiobis-(3-methyl-6-t-butylphenol) and4,4′-butylidenebis(3-methyl-6-t-butylphenol), and high molecular phenolssuch as 1,1,3-tris(2-methyl-4-hydroxy-5-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene andtetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate]methane.Organic sulfur compound-based antioxidants include dilaurylthiodipropionate, distearyl thiodipropionate and the like. Antioxidantsare preferably one or more selected from the aforementioned group ofantioxidants, and different types may be used in combination. Thecontent of the antioxidant is preferably 0.1-20 parts by weight to 100parts by weight of the thermosetting resin. More preferably, the contentof the antioxidant is 0.1-20 parts by weight to 100 parts by weight ofthe epoxy resin. If the content of the antioxidant is less than 0.1 partby weight no improvement in insulating property will be achieved, and ifit exceeds 20 parts by weight the insulating property will tend to bereduced.

As mentioned above, the prepreg of this embodiment is obtained byimpregnating a resin composition containing a resin with an imidestructure, a thermosetting resin and other components into a fiber basematerial with a thickness of 5-50 μm. FIG. 1 is a partial perspectiveview of an embodiment of a prepreg. The prepreg 100 of FIG. 1 is asheet-like prepreg composed of a fiber base material and a resincomposition impregnated in it.

Such a prepreg can be obtained by preparing a varnish by mixing,dissolving and dispersing a resin composition for prepreg in an organicsolvent, and then impregnating it into a fiber material and drying. Theorganic solvent is not particularly restricted so long as it is able todissolve or disperse the resin composition, and as examples there may bementioned dimethylacetamide, dimethylformamide, dimethylsulfoxide,N-methyl-2-pyrrolidone, 7-butyrolactone, sulfolane and cyclohexanone.

The resin composition for prepreg may be the resin composition describedabove, but preferably it contains 100 parts by weight of a resin with animide structure (siloxane-modified polyamideimide resin, polyamideimideresin having the structure represented by general formula (1) above orpolyimide resin) and 1-200 parts by weight (preferably 1-140 parts byweight) of a thermosetting resin. This will increase the vaporizationrate of the varnish solvent of the resin composition, making it possibleto achieve a residual solvent content of 5 wt % or less even at a lowtemperature of below 150° C. at which the thermosetting resin curingreaction is not promoted. The resin composition will thus havesatisfactory adhesion with the fiber base material or copper foil. Inparticular, since the siloxane-modified polyamideimide resin has thehighly heat resistant polyamideimide resin modified with siloxane, theaforementioned effect can be satisfactorily achieved. Because the amountof residual solvent can thus be minimized, the prepreg exhibits lessswelling due to solvent vaporization during the step of lamination withthe copper foil, and has excellent soldering heat resistance.

More specifically, the prepreg can be fabricated by impregnating thefiber base material with the resin composition varnish and drying it ina temperature range of 80-180° C. The fiber base material is notparticularly restricted so long as it is one used for fabrication ofmetal foil-clad laminates and multilayer printed circuit boards, and asexamples there may be mentioned fiber base materials such as wovenfabrics and nonwoven fabrics. As materials for the fiber base materialthere may be mentioned inorganic fibers such as glass, alumina,asbestos, boron, silica-alumina glass, silica glass, tirano, siliconcarbide, silicon nitride and zirconia, organic fibers such as aramid,polyetherether ketone, polyetherimide, polyethersulfone, carbon andcellulose, and blended systems thereof, among which woven fabrics ofglass fibers are preferred.

Among these, glass cloths with a thickness of 5-50 μm are preferred asfiber base materials to be used in prepregs. By using a glass cloth witha thickness of 5-50 μm, it is possible to obtain a printed circuit boardthat can be folded as desired, and which undergoes minimal dimensionalchange with the temperature and humidity of the manufacturing process.

The manufacturing conditions for the prepreg are not particularlyrestricted, but preferred are conditions wherein at least 80 wt % of thesolvent used in the varnish evaporates. The fabrication process anddrying conditions are also not particularly restricted, and for example,the temperature for drying may be 80-180° C., and the time may beadjusted in balance with the varnish gelling time. The amount of varnishimpregnated into the fiber base material is preferably such for avarnish solid content of 30-80 wt % with respect to the total amount ofsolid varnish and fiber base material.

When the prepreg is cured for use as the base material, it preferablyhas a flame retardance as a combustion distance of no greater than 100mm in the UL-94 VTM test. This condition is more preferably satisfiedwhen the resin composition contains the aforementionedphosphorus-containing compound.

The flame retardance may be evaluated by the UL-94 VTM test. The sampleused for the test may be fabricated by etching off the copper from adouble-sided copper-clad laminate prepared using the aforementionedprepreg, and then cutting it to a 200 mm length and 50 mm width,wrapping it around a mandrel with a 12.7 mm diameter and fixing it withtape at a position 125 mm from the end to form a cylinder, and finallyslipping out the mandrel.

The measurement is carried out by situating the sample vertically andclosing and anchoring the top end with a spring, and then contacting thebottom end with a 20 mm blue flame created with a methane gas burner for3 seconds and measuring the afterflame time and combustion distance. Asample exhibiting a flame retardance as a combustion distance of 100 mmor smaller in this measurement may be considered a satisfactory prepregin terms of pliability and heat resistance in a heat shock test.

[Metal Foil-Clad Laminate]

The prepreg described above may be used to obtain insulating boards,laminates and metal foil-clad laminates. Specifically, for example, theprepreg may be used alone or a plurality thereof laminated into alaminate, stacked with a metal foil on either or both sides asnecessary, and subjected to hot pressure molding at a temperature in therange of 150-280° C. or preferably 180-250° C., and a pressure in therange of 0.5-20 MPa or preferably 1-8 MPa, to fabricate an insulatingboard, laminate or metal foil-clad laminate. A metal foil-clad laminatecan be obtained when using a metal foil.

Suitable metal foils include copper foils and aluminum foils, and theymay have thicknesses of 5-200 μm. The metal foil may be a composite foilwith a three-layer structure provided with an interlayer made of nickel,nickel-phosphorus, nickel-tin alloy, nickel-iron alloy, lead, lead-tinalloy or the like, having a 0.5-15 μm copper layer and a 10-300 μmcopper layer on either side, or a composite foil with a two-layerstructure comprising aluminum and copper foils.

FIG. 2 is a partial cross-sectional view of an embodiment of a metalfoil-clad laminate. The metal foil-clad laminate 200 is obtained byheating and pressing a laminate of a prepreg 100 having a prescribednumber of layers (three in this case) and a copper foil 10 situated onboth sides thereof, and it is composed of a sheet-like board 30 composedof a laminate of a fiber-reinforced resin layer 3 and two metal foils 10adhered on either side of the board 30.

[Printed Circuit Board]

The aforementioned metal foil-clad laminate can be used to obtain aprinted circuit board. Specifically, a printed circuit board may beobtained by forming a circuit from the metal foil of the metal foil-cladlaminate (circuit formation). The circuit formation may be accomplishedby a publicly known process such as a subtractive process.

FIG. 3 is a partial cross-sectional view of an embodiment of a printedcircuit board. The printed circuit board 300 shown in FIG. 3 is composedmainly of the same board 30 as described above and two metal foils 10attached to either side of the board 30, and portions of the metal foils10 are removed to form a wiring pattern. The printed circuit board 300also has multiple through-holes 70 formed running through the circuitboard 300 in the direction approximately normal to the main surface. Thewalls of the through-holes 70 have a metal plating layer 60 formed to aprescribed thickness. Normally, predetermined circuit parts (not shown)are mounted in the printed circuit board 300.

EXAMPLES

The present invention will now be explained in greater detail byexamples, with the understanding that the invention is in no way limitedto these examples.

Synthesis Example 1a

In a 1-liter separable flask there were placed 31.0 g (0.10 mol) of3,3′,4,4′-diphenylethertetracarboxylic dianhydride, 200 g of NMP(N-methyl-2-pyrrolidone) and 200 g of m-xylene, and the mixture wasstirred at room temperature (25° C.). Next, 34.4 g (0.04 mol) of thereactive silicone oil KF-8010 (trade name of Shin-Etsu Chemical Co.,Ltd., amine equivalents: 430) as a siloxanediamine was added dropwiseusing a dropping funnel. The reaction mixture was stirred while coolingon ice, and then 24.6 g (0.06 mol) of BAPP(2,2-bis[4-(4-aminophenoxy)phenyl]propane) was added as an aromaticdiamine and stirring was continued for 2 hours at room temperature toobtain polyamic acid. The polyamic acid solution was heated to 190° C.and then heated and stirred for 20 hours, and the water produced withimide ring closure was removed by azeotropic distillation with m-xylene.Upon completion of the reaction, an NMP solution containing a polyimideresin was obtained.

Synthesis Example 2a

In a 1-liter separable flask there were placed 29.4 (0.10 mol) of3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 200 g of NMP(N-methyl-2-pyrrolidone) and 200 g of m-xylene, and the mixture wasstirred at room temperature. Next, 34.4 g (0.04 mol) of the reactivesilicone oil KF-8010 (trade name of Shin-Etsu Chemical Co., Ltd., amineequivalents: 430) as a siloxanediamine was added dropwise using adropping funnel. The reaction mixture was stirred while cooling on ice,and then 24.6 g (0.06 mol) of BAPP(2,2-bis[4-(4-aminophenoxy)phenyl]propane) was added as an aromaticdiamine and stirring was continued for 2 hours at room temperature (25°C.) to obtain polyamic acid. The polyamic acid solution was heated to190° C. and then heated and stirred for 20 hours, and the water producedwith imide ring closure was removed by azeotropic distillation withm-xylene. Upon completion of the reaction, an NMP solution containing apolyimide resin was obtained.

Example 1A

After mixing 265.0 g of an NMP solution of the polyimide resin obtainedin Synthesis Example 1A (30.2 wt % solid resin content), 40.0 g ofNC3000 (trade name of Nippon Kayaku Co., Ltd.) as an epoxy resin(dimethylacetamide solution with 50 wt % resin solid content) and 0.2 gof 2-ethyl-4-methylimidazole, the mixture was stirred for about 1 houruntil uniformity of the resin. It was then allowed to stand for 24 hoursat room temperature (25° C.) for defoaming to produce a resincomposition varnish.

Example 2a

After mixing 216.8 g of an NMP solution of the polyimide resin obtainedin Synthesis Example 2A (36.9 wt % solid resin content), 40.0 g ofNC3000 (trade name of Nippon Kayaku Co., Ltd.) as an epoxy resin(dimethylacetamide solution with 50 wt % resin solid content) and 0.2 gof 2-ethyl-4-methylimidazole, the mixture was stirred for about 1 houruntil uniformity of the resin. It was then allowed to stand for 24 hoursat room temperature (25° C.) for defoaming to produce a resincomposition varnish.

Example 3a

After mixing 248.3 g of an NMP solution of the polyimide resin obtainedin Synthesis Example 1A (30.2 wt % solid resin content), 50.0 g ofDER331L (trade name of Dainippon Ink & Chemicals, Inc.) as an epoxyresin (dimethylacetamide solution with 50 wt % resin solid content) and0.25 g of 2-ethyl-4-methylimidazole, the mixture was stirred for about 1hour until uniformity of the resin. It was then allowed to stand for 24hours at room temperature (25° C.) for defoaming to produce a resincomposition varnish.

(Fabrication of Prepreg and Metal Foil-Clad Laminate)

Each of the resin composition varnishes prepared in Examples 1A-3A wasimpregnated into a glass cloth with a thickness of 0.028 mm (trade name1037 of Asahi Shwebel Co., Ltd.), and then heated at 150° C. for 15minutes for drying to obtain a prepreg with a 70 wt % resin portion. A12 μm-thick electrolytic copper foil (trade name: F2-WS-12 by FurukawaElectric Co., Ltd.) was stacked onto both sides of the prepreg with theadhesive sides facing the prepreg, and subjected to pressing conditionsof 200° C., 90 min, 4.0 MPa to fabricate a double-sided copper cladlaminate.

Comparative Example 1a

The resin composition varnish of Example 1A was used for impregnationinto a glass cloth with a thickness of 0.10 mm (100 μm) (trade name 7010of Nitto Boseki Co., Ltd.), and was then heated at 150° C. for 25minutes for drying to obtain a prepreg with a 70 wt % resin portion. A12 μm-thick electrolytic copper foil (trade name: F2-WS-12 by FurukawaElectric Co., Ltd.) was stacked onto both sides of the prepreg with theadhesive sides facing the prepreg, and subjected to pressing conditionsof 200° C., 90 min, 4.0 MPa to fabricate a double-sided copper cladlaminate.

The obtained double-sided copper clad laminate was used for thefollowing evaluation.

(Evaluations)

(1) The copper foil peel strength of the double-sided copper cladlaminate was measured.(2) Upon immersion for 5 minutes in soldering baths at 260° C., 288° C.and 300° C., abnormalities such as swelling or peeling were observed.The evaluation was made in the following manner.◯: No abnormalities, X Abnormalities.(3) The copper foil was etched for removal and the laminate was foldedto evaluate the pliability. The evaluation was made in the followingmanner.◯: No fracture, X Fracture.(4) A circuit was formed on the double-sided copper clad laminate toprepare a daisy chain pattern test piece. Each test piece was subjectedto 1000 cycles of a heat shock test with each cycle being −65° C./30min, 125° C./30 min, and the change in resistance was measured. Theevaluation was made in the following manner.◯: No greater than 10% resistance change, X: Greater than 10% resistancechange.The obtained results are shown in Table 1.

TABLE 1 Comp. Evaluation Units Example 1A Example 2A Example 3A Example1A Polyimide resin — Synthesis Synthesis Synthesis Synthesis Example 1AExample 2A Example 1A Example 1A Epoxy resin — NC3000 NC3000 DER331LNC3000 Polyimide/epoxy pts. by wt. 80/20 80/20 75/25 80/20 Pliability —∘ ∘ ∘ x Soldering heat resistance — ∘ ∘ ∘ ∘ Heat shock test — ∘ ∘ ∘ ∘Copper foil peel strength kN/m 1.2 0.9 1.0 1.1

All of the prepregs of Examples 1A-3A were satisfactory with high valuesof 0.9-1.2 kN/m for the copper foil peel strength. Also, the solderingheat resistance (260° C. soldering, 288° C. soldering, 300° C.soldering) was 5 minutes or longer at all temperatures, and noabnormalities such as swelling or peeling were observed. In the heatshock test, the resistance change was within 10% at 1000 cycles,indicating satisfactory connection reliability. Also, the pliability wassufficient to allow folding as desired.

In contrast, the double-sided copper clad laminate of ComparativeExample 1A had no pliability, and cracks formed in the glass cloth andresin sections upon folding. Warping was also observed.

Synthesis Example 1B

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 14.9 g (0.06 mol) of DDS(diaminodiphenylsulfone) as a diamine with two or more aromatic rings,43.0 g (0.05 mol) of the reactive silicone oil KF-8010 (trade name ofShin-Etsu Chemical Co., Ltd., amine equivalents: 430) as asiloxanediamine, 72.0 g (0.36 mol) of JEFFAMINE D2000 (trade name of SanTechno Chemical Co., Ltd., amine equivalents: 1000) as an aliphaticdiamine, 11.3 g (0.054 mol) of WONDAMINE (trade name of New JapanChemical Co., Ltd.) as a diamine represented by general formula (4) and80.7 g (0.42 mol) of TMA (trimellitic anhydride), with 589 g of NMP(N-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixturewas stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 55.1 g (0.22 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing a polyamideimideresin.

Synthesis Example 2B

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 14.9 g (0.06 mol) of DDS(diaminodiphenylsulfone) as a diamine with two or more aromatic rings,51.6 g (0.06 mol) of the reactive silicone oil KF-8010 (trade name ofShin-Etsu Chemical Co., Ltd., amine equivalents: 430) as asiloxanediamine, 52.0 g (0.26 mol) of JEFFAMINE D2000 (trade name of SanTechno Chemical Co., Ltd., amine equivalents: 1000) as an aliphaticdiamine, 11.3 g (0.054 mol) of WONDAMINE (trade name of New JapanChemical Co., Ltd.) as a diamine represented by general formula (4) and80.7 g (0.42 mol) of TMA (trimellitic anhydride), with 575 g of NMP(N-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixturewas stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 55.1 g (0.22 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing a polyamideimideresin.

Synthesis Example 3B

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 14.9 g (0.06 mol) of DDS(diaminodiphenylsulfone) as a diamine with two or more aromatic rings,43.0 g (0.05 mol) of the reactive silicone oil KF-8010 (trade name ofShin-Etsu Chemical Co., Ltd., amine equivalents: 430) as asiloxanediamine, 72.0 g (0.36 mol) of JEFFAMINE D2000 (trade name of SanTechno Chemical Co., Ltd., amine equivalents: 1000) as an aliphaticdiamine, 11.3 g (0.054 mol) of WONDAMINE (trade name of New JapanChemical Co., Ltd.) as a diamine represented by general formula (4) and80.7 g (0.42 mol) of TMA (trimellitic anhydride), with 599 g of NMP(N-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixturewas stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 60.1 g (0.24 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing a polyamideimideresin.

Example 1B

After mixing 250.0 g of an NMP solution of the polyamideimide resin(PAI) of Synthesis Example 1B (32 wt % solid resin content), 40.0 g ofNC3000 (trade name of Nippon Kayaku Co., Ltd.) as an epoxy resin (Ep)(dimethylacetamide solution with 50 wt % solid resin content) and 0.2 gof 2-ethyl-4-methylimidazole, the mixture was stirred for about 1 houruntil uniformity of the resin and then allowed to stand for 24 hours atroom temperature (25° C.) for defoaming to obtain a resin compositionvarnish.

Example 2B

A resin composition varnish was obtained in the same manner as Example1B, except that an NMP solution of the polyamideimide resin (PAI) ofSynthesis Example 2B was used instead of the polyamideimide resin (PAI)of Synthesis Example 1B.

Example 3B

A resin composition varnish was obtained in the same manner as Example1B, except that an NMP solution of the polyamideimide resin (PAI) ofSynthesis Example 3B was used instead of the polyamideimide resin (PAI)of Synthesis Example 1B.

Reference Example 1B

A resin composition varnish was obtained in the same manner as Example1B, except that an NMP solution of KS6600 (trade name of HitachiChemical Co., Ltd.) as a polyamideimide resin (PAI) without thestructure of general formula (1) was used instead of the polyamideimideresin (PAI) of Synthesis Example 1B.

(Fabrication of Prepreg and Metal Foil-Clad Laminate)

The resin composition varnishes prepared in Examples 1B-3B and ReferenceExample 1B were each impregnated into a 0.028 mm-thick glass cloth(trade name: 1037 by Asahi Shwebel Co., Ltd.), and then heated at 150°C. for 15 minutes for drying to obtain a prepreg with a 70 wt % resinportion.

A 12 μm-thick electrolytic copper foil (trade name: F2-WS-12 by FurukawaElectric Co., Ltd.) was stacked onto both sides of the prepreg with theadhesive sides facing the prepreg, and subjected to pressing conditionsof 230° C., 90 min, 4.0 MPa to fabricate a double-sided copper cladlaminate. The fabricated double-sided copper clad laminate was used forthe following evaluation.

(Evaluations)

(1) The copper foil peel strength of the double-sided copper cladlaminate was measured.(2) The time until abnormalities such as swelling or peeling appearedafter immersion in soldering baths at 260° C. and 288° C. was measured.(3) The copper foil was etched for removal and the laminate was foldedto evaluate the pliability. The evaluation was made in the followingmanner.◯: No fracture, X Fracture.(4) The laminate with the copper foil removed on one side by etching wassubjected to moisture absorption treatment for one hour with PCTsaturation conditions of 121° C., 2 atmospheres, and then immersed for20 seconds in a soldering bath at 260° C., upon which abnormalities suchas swelling or peeling of the laminate were observed (PCT resistance).The evaluation was made in the following manner.◯: No abnormalities, X Abnormalities.The obtained results are shown in Table 2.

TABLE 2 Reference Evaluation Units Example 1B Example 2B Example 3BExample 1B PAI — Synthesis Synthesis Synthesis KS6600 Example 1B Example2B Example 3B PAI/Ep pts. by wt. 80/20 80/20 80/20 80/20 Pliability — ∘∘ ∘ x 260° C. soldering sec. >300 >300 >300 150 288° C. solderingsec. >300 >300 >300 60 PCT resistance — ∘ ∘ ∘ x Copper foil peel kN/m1.0 0.8 0.9 0.6 strength

All of the prepregs of Examples 1B-3B containing polyamideimide resinswith structures according to general formula (1) were satisfactory withhigh values of 0.8-1.0 kN/m for the copper foil peel strength. Also, thesoldering heat resistance (260° C. soldering, 288° C. soldering) was 5minutes or longer at both temperatures, and no abnormalities such asswelling or peeling were observed. Also, the pliability was sufficientto allow folding of the laminate as desired. Moreover, no abnormalitiessuch as swelling or peeling were observed in the soldering bathimmersion at 260° C. for 20 seconds when moisture absorption treatmentwas carried out under PCT saturation conditions of 121° C., 2atmospheres.

In contrast, the prepreg or metal foil-clad laminate of ReferenceExample 1B had a low copper foil peel strength of 0.6 kN/m. Furthermore,the pliability was poor and fracturing occurred when the laminate wasfolded. In addition, the soldering heat resistance and PCT resistancewere inferior, and abnormalities such as swelling and peeling wereobserved.

Synthesis Example 1C

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 29.8 g (0.12 mol) of DDS(diaminodiphenylsulfone) as a diamine with two or more aromatic rings,34.4 g (0.04 mol) of the reactive silicone oil KF-8010 (trade name ofShin-Etsu Chemical Co., Ltd., amine equivalents: 430) as asiloxanediamine, 80.0 g (0.04 mol) of JEFFAMINE D2000 (trade name of SanTechno Chemical Co., Ltd., amine equivalents: 1000) and 80.7 g (0.42mol) of TMA (trimellitic anhydride), with 605 g of NMP(N-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixturewas stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 60.1 g (0.24 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing asiloxane-modified polyamideimide resin.

Synthesis Example 2C

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 41.1 g (0.10 mol) of BAPP(2,2-bis[4-(4-aminophenoxy)phenyl]propane) as a diamine with two or morearomatic rings, 43.0 g (0.05 mol) of the reactive silicone oil KF-8010(trade name of Shin-Etsu Chemical Co., Ltd., amine equivalents: 430) asa siloxanediamine, 100.0 g (0.05 mol) of JEFFAMINE D2000 (trade name ofSan Techno Chemical Co., Ltd., amine equivalents: 1000) and 80.7 g (0.42mol) of TMA (trimellitic anhydride), with 603 g of NMPN-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixture wasstirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 60.1 g (0.24 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing asiloxane-modified polyamideimide resin.

Example 1C

After mixing 250.0 g of an NMP solution of the siloxane-modifiedpolyamideimide resin (PAI) of Synthesis Example 1C (32 wt % solid resincontent), 40.0 g of NC3000 (trade name of Nippon Kayaku Co., Ltd.) as anepoxy resin (Ep) (dimethylacetamide solution with 50 wt % solid resincontent) and 0.2 g of 2-ethyl-4-methylimidazole, the mixture was stirredfor about 1 hour until uniformity of the resin. Next, 20 g of OP930(Clariant Japan) was added as a phosphorus-containing compound(phosphorus-based flame retardant) in the form of a methyl ethyl ketoneslurry, and mixing was continued for one hour. The mixture was thenallowed to stand for 24 hours at room temperature (25° C.) for defoamingto produce a resin composition varnish with a phosphorus content of 3.92wt %.

Example 2C

After mixing 228.6 g of an NMP solution of the siloxane-modifiedpolyamideimide resin (PAI) of Synthesis Example 2C (35 wt % solid resincontent), 40.0 g of NC3000 (trade name of Nippon Kayaku Co., Ltd.) as anepoxy resin (Ep) (dimethylacetamide solution with 50 wt % solid resincontent) and 0.2 g of 2-ethyl-4-methylimidazole, the mixture was stirredfor about 1 hour until uniformity of the resin. Next, 20 g of OP930(Clariant Japan) was added as a phosphorus-containing compound(phosphorus-based flame retardant) in the form of a methyl ethyl ketoneslurry, and mixing was continued for one hour. The mixture was thenallowed to stand for 24 hours at room temperature (25° C.) for defoamingto produce a resin composition varnish with a phosphorus content of 3.92wt %.

Example 3C

After mixing 250.0 g of an NMP solution of the siloxane-modifiedpolyamideimide resin (PAI) of Synthesis Example 1C (32 wt % solid resincontent), 40.0 g of DER331L (trade name of The Dow Chemical Company) asan epoxy resin (Ep) (dimethylacetamide solution with 50 wt % solid resincontent) and 0.2 g of 2-ethyl-4-methylimidazole, the mixture was stirredfor about 1 hour until uniformity of the resin. Next, 20 g of OP930(Clariant Japan) was added as a phosphorus-containing compound(phosphorus-based flame retardant) in the form of a methyl ethyl ketoneslurry, and mixing was continued for one hour. The mixture was thenallowed to stand for 24 hours at room temperature (25° C.) for defoamingto produce a resin composition varnish with a phosphorus content of 3.92wt %.

Example 4C

After mixing 250.0 g of an NMP solution of the siloxane-modifiedpolyamideimide resin (PAI) of Synthesis Example 1C (32 wt % solid resincontent), 40.0 g of DER331L (trade name of The Dow Chemical Company) asan epoxy resin (Ep) (dimethylacetamide solution with 50 wt % solid resincontent) and 0.2 g of 2-ethyl-4-methylimidazole, the mixture was stirredfor about 1 hour until uniformity of the resin. Next, 30 g of OP930(Clariant Japan) as a phosphorus-containing compound (phosphorus-basedflame retardant) and 10.0 g of HCA-HQ (trade name of Sanko ChemicalIndustry Co., Ltd.) were added in the form of a methyl ethyl ketoneslurry, and mixing was continued for one hour. The mixture was thenallowed to stand for 24 hours at room temperature (25° C.) for defoamingto produce a resin composition varnish with a phosphorus content of 5.72wt %.

Reference Example 1C

A resin composition with a phosphorus content of 0.06 wt % was preparedin the same manner as Example 1C, except that a liquid phosphoruscompound (trade name: REOFOS 110, product of Ajinomoto Co., Inc.) wasused as the phosphorus-containing compound.

Reference Example 2C

A resin composition with a phosphorus content of 3.92 wt % was preparedin the same manner as Example 1C, except for using 114.3 g of an NMPsolution of the siloxane-modified polyamideimide resin (PAI) ofSynthesis Example 1C (32 wt % solid resin content) and 120.0 g of NC3000(trade name of Nippon Kayaku Co., Ltd.) as an epoxy resin (Ep)(dimethylacetamide solution with 50 wt % solid resin content).

(Fabrication of Prepreg and Metal Foil-Clad Laminate)

The resin composition varnishes prepared in Examples 1C-4C and ReferenceExample 1C, 2C were each impregnated into a 0.028 mm-thick glass cloth(trade name: 1037 by Asahi Shwebel Co., Ltd.), and then heated at 150°C. for 15 minutes for drying to obtain a prepreg with a 70 wt % resinportion.

A 12 μm-thick electrolytic copper foil (trade name: F2-WS-12 by FurukawaElectric Co., Ltd.) was stacked onto both sides of the prepreg with theadhesive sides facing the prepreg, and subjected to pressing conditionsof 230° C., 90 min, 4.0 MPa to fabricate a double-sided copper cladlaminate. The fabricated double-sided copper clad laminate was used forthe following evaluation.

(Evaluations)

(1) The copper foil peel strength of the double-sided copper cladlaminate was measured.(2) The time until abnormalities such as swelling or peeling appearedafter immersion in soldering baths at 260° C. and 288° C. was measured.(3) The copper foil was etched for removal and the laminate was foldedto evaluate the pliability. The evaluation was made in the followingmanner.◯: No fracture, Δ: Some fracture, X: Fracture.(4) The flame retardance was evaluated by a UL-94 VTM test.Specifically, first the copper was etched off from the double-sidedcopper clad laminate, and a 200 mm long, 50 mm wide piece was cut outand wrapped around a 12.7 mm-diameter mandrel, and after fixing it withtape at a position 125 mm from the end to form a cylinder, the mandrelwas slipped out to obtain a sample. The sample was then situatedvertically and the top end was closed and anchored with a spring, afterwhich the bottom end was contacted with a 20 mm blue flame created witha methane gas burner for 3 seconds and the afterflame time andcombustion distance were measured.(5) A circuit was formed on the double-sided copper clad laminate toprepare a daisy chain pattern test piece. Each test piece was subjectedto 1000 cycles of a heat shock test with each cycle being −65° C./30min, 125° C./30 min, and the change in resistance was measured. Theevaluation was made in the following manner.◯: No greater than 10% resistance change, X: Greater than 10% resistancechange.The evaluation results are shown in Table 3.

TABLE 3 Reference Reference Evaluation Units Example 1C Example 2CExample 3C Example 4C Example 1C Example 2C PAI — Synthesis SynthesisSynthesis Synthesis Synthesis Synthesis Example 1C Example 2C Example 1CExample 1C Example 1C Example 1C PAI/Ep pts. by 80/20 80/20 80/20 80/2080/20 37/60 wt. P-containing — OP930 OP930 OP930 OP930 REOFOS OP930compound HCA-HQ 110 P content wt % 3.92 3.92 3.92 5.72 0.06 3.92Pliability — ∘ ∘ ∘ ∘ Δ x Flame retardance — VTM-0 VTM-0 VTM-0 VTM-0 HB —Combustion mm 80 80 80 80 125 — distance* 260° C. solderingsec. >300 >300 >300 >300 40 50 288° C. solderingsec. >300 >300 >300 >300 10 20 Heat shock test — ∘ ∘ ∘ ∘ x x Copper foilpeel kN/m 1.0 1.0 0.9 0.8 0.6 0.5 strength *UL-94 VTM test

All of the prepregs of Examples 1C-4C were satisfactory with high valuesof 0.8-1.0 kN/m for the copper foil peel strength. Also, the solderingheat resistance (260° C. soldering, 288° C. soldering) was 5 minutes orlonger at both temperatures, and no abnormalities such as swelling orpeeling were observed. The combustion distance of each 12.7 mm-diametertest piece in the UL94 VTM test was less than 100 mm (80 mm), and theflame retardance was VTM-0 in all cases. In the heat shock test, theresistance change was within 10% at 1000 cycles, indicating satisfactoryconnection reliability.

In contrast, the copper foil peel strength of the prepreg of ReferenceExample 1C which had a phosphorus content of 0.06 wt % was a low valueof 0.6 kN/m, while the flame retardance was HB and the combustiondistance was 125 mm. Also, Reference Example 2C which contained athermosetting (epoxy) resin at 162 parts by weight with respect to 100parts by weight of the polyamideimide resin had poor pliability andexhibited fracturing when the laminate was folded. Thus, no sample couldbe prepared for flame retardance evaluation, and measurement of thecombustion distance was impossible. Also, both Reference Examples 1C and2C had inferior soldering heat resistance, abnormalities such asswelling and peeling were observed, and the resistance value variedconsiderably in the heat shock test. In the heat shock test, the changein resistance value was greater than 10% at 200 cycles with ReferenceExample 1C and at 100 cycles with Reference Example 2C.

Synthesis Example 1D

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 12.4 g (0.05 mol) of DDS(diaminodiphenylsulfone) as a diamine with two or more aromatic rings,51.6 g (0.06 mol) of the reactive silicone oil KF-8010 (trade name ofShin-Etsu Chemical Co., Ltd., amine equivalents: 430) as asiloxanediamine, 72.0 g (0.036 mol) of JEFFAMINE D2000 (trade name ofSan Techno Chemical Co., Ltd., amine equivalents: 1000), 11.34 g (0.054mol) of WONDAMINE (trade name of New Japan Chemical Co., Ltd.) and 80.68g (0.42 mol) of TMA (trimellitic anhydride), with 612 g of NMP(N-methyl-2-pyrrolidone) as an aprotic polar solvent, and the mixturewas stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 60.1 g (0.24 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing asiloxane-modified polyamideimide resin.

Synthesis Example 2D

In a 1-liter separable flask equipped with a cock-stoppered 25-ml watermeasuring receptacle connected to a reflux condenser, and a thermometerand stirrer, there were charged 24.63 g (0.06 mol) of BAPP(2,2-bis[4-(4-aminophenoxy)phenyl]propane) as a diamine with two or morearomatic rings, 124.6 g (0.14 mol) of the reactive silicone oil KF-8010(trade name of Shin-Etsu Chemical Co., Ltd., amine equivalents: 445) asa siloxanediamine and 80.68 g (0.42 mol) of TMA (trimellitic anhydride),with 539 g of NMP N-methyl-2-pyrrolidone) as an aprotic polar solvent,and the mixture was stirred at 80° C. for 30 minutes.

Next, 150 ml of toluene was loaded as an aromatic hydrocarbon forazeotropic distillation with water, and the temperature was raised for 2hours of reflux at about 160° C. When approximately 7.2 ml of water hadaccumulated in the water measuring receptacle, cessation of waterdistillation was confirmed, and the temperature was raised to about 190°C. for removal of the toluene while removing the distillate accumulatedin the water measuring receptacle. Next, the solution was returned toroom temperature (25° C.), and 60.07 g (0.24 mol) of MDI(4,4′-diphenylmethanediisocyanate) was loaded as an aromaticdiisocyanate for 2 hours of reaction at 190° C. Upon completion of thereaction there was obtained an NMP solution containing asiloxane-modified polyamideimide resin.

Example 1D

After mixing 218.75 g of an NMP solution of the siloxane-modifiedpolyamideimide resin of Synthesis Example 1D (32 wt % solid resincontent), 60.0 g of NC3000 (epoxy resin, trade name of Nippon KayakuCo., Ltd.) as a thermosetting resin (dimethylacetamide solution with 50wt % solid resin content), 0.3 g of 2-ethyl-4-methylimidazole and 0.5 gof 4,4′-butylidenebis(3-methyl-6-t-butylphenol) as a hinderedphenol-based antioxidant, the mixture was stirred for about 1 hour untiluniformity of the resin. Next, 20 g of OP930 (trade name of ClariantJapan) was added as a phosphorus-containing filler in the form of aslurry with 40 g of methyl ethyl ketone, and mixing was continued forone hour. The mixture was then allowed to stand for 24 hours at roomtemperature (25° C.) for defoaming to produce a resin compositionvarnish.

Example 2D

After mixing 218.75 g of an NMP solution of the siloxane-modifiedpolyamideimide resin of Synthesis Example 1D (32 wt % solid resincontent), 60.0 g of DER331L (epoxy resin, trade name of The Dow ChemicalCompany) as a thermosetting resin (dimethylacetamide solution with 50 wt% solid resin content), 0.3 g of 2-ethyl-4-methylimidazole and 0.5 g of1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane as a hinderedphenol-based antioxidant, the mixture was stirred for about 1 hour untiluniformity of the resin. Next, 15 g of OP930 (trade name of ClariantJapan) was added as a phosphorus-containing filler in the form of aslurry with 30 g of methyl ethyl ketone, and mixing was continued forone hour. The mixture was then allowed to stand for 24 hours at roomtemperature (25° C.) for defoaming to produce a resin compositionvarnish.

Example 3D

After mixing 218.75 g of an NMP solution of the siloxane-modifiedpolyamideimide resin of Synthesis Example 1D (32 wt % solid resincontent), 60.0 g of ZX-1548-2 (epoxy resin, trade name of Tohto KaseiCo., Ltd.) as a thermosetting resin (dimethylacetamide solution with 50wt % solid resin content), 0.3 g of 2-ethyl-4-methylimidazole and 0.5 gof dilauryl thiopropionate as an organic sulfur compound-basedantioxidant, the mixture was stirred for about 1 hour until uniformityof the resin. Next, 20 g of OP930 (trade name of Clariant Japan) wasadded as a phosphorus-containing filler in the form of a slurry with 40g of methyl ethyl ketone, and mixing was continued for one hour. Themixture was then allowed to stand for 24 hours at room temperature (25°C.) for defoaming to produce a resin composition varnish.

Example 4D

A resin composition varnish was produced in the same manner as Example1D, except that 200.0 g of an NMP solution of the siloxane-modifiedpolyamideimide resin of Synthesis Example 2D (35 wt % solid resincontent) was used instead of the siloxane-modified polyamideimide resinof Synthesis Example 1D.

Example 5D

A resin composition varnish was produced in the same manner as Example2D, except that 200.0 g of an NMP solution of the siloxane-modifiedpolyamideimide resin of Synthesis Example 2D (35 wt % solid resincontent) was used instead of the siloxane-modified polyamideimide resinof Synthesis Example 1D.

Reference Example 1D

A resin composition varnish was produced in the same manner as Example1D, except for not adding the hindered phenol-based antioxidant4,4′-butylidenebis(3-methyl-6-t-butylphenol).

Reference Example 2D

A resin composition varnish was produced in the same manner as Example2D, except for not adding the hindered phenol-based antioxidant1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.

Reference Example 3D

A resin composition varnish was produced in the same manner as Example3D, except for not adding the organic sulfur compound-based antioxidantdilauryl thiopropionate.

Reference Example 4D

A resin composition varnish was produced in the same manner as Example4D, except for not adding the hindered phenol-based antioxidant4,4′-butylidenebis(3-methyl-6-t-butylphenol).

Reference Example 5D

A resin composition varnish was produced in the same manner as Example5D, except for not adding the hindered phenol-based antioxidant1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane.

(Fabrication of Prepreg and Double-Sided Copper Clad Laminate)

The resin composition varnishes prepared in Examples 1D-5D and ReferenceExamples 1D-5D were each impregnated into a 0.028 mm-thick glass cloth(trade name: 1037 by Asahi Shwebel Co., Ltd.), and then heated at 150°C. for 15 minutes for drying to obtain a prepreg with a 70 wt % solidresin portion. A 12 μm-thick electrolytic copper foil (trade name:F2-WS-12 by Furukawa Electric Co., Ltd.) was stacked onto both sides ofa prepreg with the adhesive sides facing the prepreg, and subjected topressing conditions of 230° C., 90 min, 4.0 MPa to fabricate adouble-sided copper clad laminate. Also, eight prepregs were stackedtogether, and a 12 μm-thick electrolytic copper foil (trade name:F2-WS-12 by Furukawa Electric Co., Ltd.) was stacked onto both sidesthereof with the adhesive sides facing the prepreg, and then subjectedto pressing conditions of 230° C., 90 min, 4.0 MPa to fabricate adouble-sided copper clad laminate. The double-sided copper clad laminatefabricated with a single prepreg was subjected to the followingevaluations (1) to (4). The double-sided copper clad laminate fabricatedwith eight prepregs was subjected to the following evaluations (5) and(6).

(Evaluations)

(1) The copper foil peel strength of the double-sided copper cladlaminate was measured.(2) The time until abnormalities such as swelling or peeling appearedafter immersion in soldering baths at 260° C. and 300° C. was measured.(3) The copper foil was etched for removal and the laminate was foldedto evaluate the pliability. The evaluation was made in the followingmanner.◯: No fracture, Δ: Some fracture, X: Fracture.(4) The flame retardance was evaluated by a UL-94 VTM test.Specifically, first the copper was etched off from the double-sidedcopper clad laminate, and a 200 mm long, 50 mm wide piece was cut outand wrapped around a 12.7 mm-diameter mandrel, and after fixing it withtape at a position 125 mm from the end to form a cylinder, the mandrelwas slipped out to obtain a sample. The sample was then situatedvertically and the top end was closed and anchored with a spring, afterwhich the bottom end was contacted with a 20 mm blue flame created witha methane gas burner for 3 seconds and the combustion distance wasmeasured. Samples with a combustion distance of 100 mm or less wereassigned a flame retardance of VTM-0.(5) A circuit was formed on the double-sided copper clad laminate toprepare a daisy chain pattern test piece. Each test piece was subjectedto 1000 cycles of a heat shock test with each cycle being −65° C./30min, 125° C./30 min, and the change in resistance was measured. Theevaluation was made in the following manner.OK: No greater than 10% resistance change, NG: Greater than 10%resistance change.(6) A circuit was formed on the double-sided copper clad laminate andused for a migration test. The through-holes were created with a 0.9mm-diameter drill under conditions of 60,000 rpm, 1.800 mm/min feedrate. The spacing between hole walls was 350 μm, and the insulationresistance of 400 holes (200 locations betweenthrough-hole/through-hole) was periodically measured for each sample.The test conditions were an environment of 85° C./90% RH and applicationof 100 V, and the measurement was carried out for a number of days untilinterruption of current between the through-holes occurred. Measurementof the insulation resistance was conducted at 100V/1 min, andinterruption of current was defined as less than 10⁸Ω. The evaluationresults are shown in Table 4.

TABLE 4 Reference Reference Reference Reference Reference ExampleExample Example Example Example Example Example Example Example ExampleEvaluation Units 1D 2D 3D 4D 5D 1D 2D 3D 4D 5D Number ofDays >60 >60 >60 >60 >60 30 7 10 35 11 days to current interruptionCopper foil kN/m 1.1 0.9 1.0 0.8 0.9 0.8 0.8 0.8 0.8 0.8 peel strength260° C. sec. >300 >300 >300 >300 >300 >300 >300 >300 >300 >300 solderingheat resistance 300° C.sec. >300 >300 >300 >300 >300 >300 >300 >300 >300 >300 soldering heatresistance Heat shock — OK OK OK OK OK OK OK OK OK OK test Pliability —∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ Flame — VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0 VTM-0VTM-0 VTM-0 VTM-0 retardance

The copper foil peel strengths of the double-sided copper clad laminatesof Examples 1D-5D were satisfactory high values of 0.8-1.1 kN/m. Also,the soldering heat resistance (260° C. soldering, 300° C. soldering) was5 minutes or longer at both temperatures, and no abnormalities such asswelling or peeling were observed. The combustion distance of each 12.7mm-diameter test piece in the UL94 VTM test was less than 100 mm, andthe flame retardance was VTM-0 in all cases. In the heat shock test, theresistance change was within 10% at 1000 cycles, indicating satisfactoryconnection reliability. Also, the pliability was sufficient to allowfolding as desired. Also, Examples 1D-5D which included the (c)antioxidant exhibited no interruption of current for more than 60 days,and had higher insulation properties than Reference Examples 1D-5D. Theinsulation resistance value was 10¹¹Ω or greater after 60 days withExamples 1D-5D.

1. A prepreg obtained by impregnating a resin composition comprising aresin with an imide structure and a thermosetting resin into a fiberbase material with a thickness of 5-50 μm, said prepreg having aproperty that it can be bent.
 2. A prepreg according to claim 1, whereinsaid resin with an imide structure has a siloxane structure.
 3. Aprepreg according to claim 1, wherein said resin with an imide structurealso has a structure represented by the following general formula (1):


4. A prepreg according to claim 1, wherein said resin with an imidestructure is a polyamideimide resin.
 5. A prepreg according to claim 1,wherein said resin with an imide structure is a polyamideimide resinobtained by reacting a diisocyanate compound with a mixture containing adiimidedicarboxylic acid obtained by reacting a mixture containing asiloxanediamine and a diamine represented by the following generalformula (2a) or (2b) with trimellitic anhydride:

[wherein X²¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, a single bond, a divalent group represented by thefollowing general formula (3a) or a divalent group represented by thefollowing general formula (3b), X²² represents a C1-3 aliphatichydrocarbon group, C1-3 halogenated aliphatic hydrocarbon group,sulfonyl group, ether group or carbonyl group, and R²¹, R²² and R²³ eachindependently or identically represent hydrogen, hydroxyl, methoxy,methyl or halogenated methyl:

(wherein X³¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, or a single bond)].
 6. A prepreg according to claim 1,wherein said resin with an imide structure is a polyamideimide resinobtained by reacting a diisocyanate compound with a mixture containing adiimidedicarboxylic acid obtained by reacting a mixture containing adiamine represented by the following general formula (4), asiloxanediamine and a diamine represented by the following generalformula (5a) or (5b), with trimellitic anhydride:

[wherein X⁵¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, a single bond, a divalent group represented by thefollowing general formula (6a) or a divalent group represented by thefollowing general formula (6b), X⁵² represents a C1-3 aliphatichydrocarbon group, C1-3 halogenated aliphatic hydrocarbon group,sulfonyl group, ether group or carbonyl group, and R⁵, R⁵² and R⁵³ eachindependently or identically represent hydrogen, hydroxyl, methoxy,methyl or halogenated methyl:

(wherein X⁶¹ represents a C1-3 aliphatic hydrocarbon group, C1-3halogenated aliphatic hydrocarbon group, sulfonyl group, ether group orcarbonyl group, or a single bond)].
 7. A prepreg according to claim 1,wherein said resin with an imide structure is a polyimide resin havingthe structure represented by the following general formula (7) or apolyimide resin having the structure represented by the followinggeneral formula (7) and the structure represented by the followinggeneral formula (8):

[wherein Ar¹ represents a tetravalent aromatic group, Ar² represents adivalent aromatic group, R⁷¹ and R⁷² each independently or identicallyrepresent a divalent hydrocarbon group, R⁷³, R⁷⁴, R⁷⁵ and R⁷⁶ eachindependently or identically represent a C1-6 hydrocarbon group, and nrepresents an integer of 1-50].
 8. A prepreg according to claim 1,wherein said resin with an imide structure is a polyamideimide resinhaving the structure represented by the following general formula (9):

[wherein R⁹¹, R⁹², R⁹³ and R⁹⁴ each represent a carbon atom from aportion of the cyclic or linear structure composing the polyamideimideresin].
 9. A prepreg according to claim 1, wherein said thermosettingresin is an epoxy resin.
 10. A prepreg according to claim 1, whereinsaid thermosetting resin is an epoxy resin with two or more glycidylgroups.
 11. A prepreg according to claim 1, wherein said resincomposition further contains a phosphorus-containing compound, and saidresin composition contains said thermosetting resin at 1-140 parts byweight with respect to 100 parts by weight of said resin with an imidestructure, and phosphorus at 0.1-5 wt % of the total weight of the resinsolid portion.
 12. A prepreg according to claim 1, wherein said resincomposition further contains a hindered phenol-based or organic sulfurcompound-based antioxidant.
 13. A metal foil-clad laminate obtained bystacking a prescribed number of prepregs according to claim 1, situatinga metal foil on either or both sides thereof and subjecting the stack toheat and pressure.
 14. A printed circuit board obtained by forming acircuit in the metal foil of the metal foil-clad laminate according toclaim
 13. 15. The printed circuit board according to claim 14, having aproperty that it can be folded.